This invention relates generally to a gas turbine engine and specifically to a fuel nozzle for the gas turbine engine for delivering a liquid fuel.
Modern gas turbine engines increasingly must meet conflicting standards of efficiency and emissions. Lean premixed prevaporized (LPP) combustion is one manner of greatly reducing emissions. In a LPP system, air and fuel are mixed upstream in advance of being exposed to an ignition source. A fuel air mixture having air in excess of that needed for combustion is formed. The excess air reduces temperature of combustion in a primary combustion zone and thus the production of NOx. An example of a lean premixed combustion system is shown in U.S. Pat. No. 5,826,423 issued to Lockyer et al on Oct. 27, 1998.
However, LPP combustion typically is less stable than a combustion system operating with an air fuel ratio near stoichiometric or in a rich condition. Weak extinction or extinguishing of the flame becomes more prevalent during lean premixed combustion. LPP combustion systems may use pilot injection of fuel to enrich the mixture and provide more stable combustion and avoid weak extinction limits. Further, LPP systems require additional time for the fuel to atomize and mix thoroughly with the air. The additional time allows an opportunity for localized autoignition of fuel droplets. A hot recirculating gas may also cause combustion of fuel causing a flashback phenomenon.
Due to the unstable nature of LPP combustion, making any changes in an air flow path through the combustion system typically requires extensive effort to avoid the problems set out above. One typical change may include changing fuels supplied for combustion. For instance, a lean premixed gaseous system may use a plurality of fuel spokes in a premixing region of a fuel injector. Switching that same combustion system to a LPP combustion system may create significant changes in air flow paths in the fuel nozzle. These changes in air flow paths may lead to instabilities as set out above.
The present invention is directed to overcoming one or more of the problems as set forth above.
In an embodiment of the present invention a fuel nozzle for a gas turbine engine has a center body. A barrel portion is positioned radially distal from the center body. At least one swirler vane is positioned between the center body and the barrel portion. The swirler vane has a pressure surface portion, a suction surface portion, a trailing edge distal from a leading edge. The pressure surface portion and the suction surface portion extend between the leading edge portion and the trailing edge portion. A liquid fuel passage passes through the swirler vane. A liquid fuel jet on either the pressure surface, the suction surface, or both fluidly communicates with the liquid fuel passage.
In another embodiment the present invention a method for operating a fuel nozzle for a gas turbine engine includes introducing a liquid fuel flow from the surface of a swirler vane. An air flow is directed across the swirler vane to atomize the fuel flow. The fuel flow and air flow then mix over some predetermined length L.